<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <div id="father">
        <h1>标题一</h1>
        <p id="p1">p1</p>
        <p class="p2">p2</p>
    </div>

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    var p1 = document.getElementById('p1');
    var p2 = document.getElementsByClassName('p2');
    var father = document.getElementById('father');

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    father.firstChild;
    father.lastChild;
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</body>
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